Investment Securities (Related Adjustments for Nonmarketable Equity Securities) (Detail) - Nonmarketable equity securities - Measurement alternative - JPY (¥) ¥ in Millions	12 Months Ended
Mar. 31, 2026	Mar. 31, 2025	Mar. 31, 2024
Investment Securities [Line Items]
Measurement alternative impairment losses	¥ (22,633)	¥ (37,469)	¥ (11,943)
Measurement alternative downward changes for observable prices	0	0	(1,567)
Measurement alternative upward changes for observable prices	12,222	8,060	¥ 882
Cumulative impairment losses	85,549	65,989
Cumulative downward changes for observable prices	2,961	2,961
Cumulative upward changes for observable prices	¥ 77,877	¥ 66,132

Investment Securities [Line Items]

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- Definition

Amount of loss from downward price adjustment on investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 321
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (b)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479536/321-10-50-3

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Amount of cumulative loss from downward price adjustment on investment in equity security without readily determinable fair value.

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- Definition

Amount of impairment loss on investment in equity security without readily determinable fair value.

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- Definition

Amount of cumulative impairment loss on investment in equity security without readily determinable fair value.

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- Definition

Amount of gain from upward price adjustment on investment in equity security without readily determinable fair value.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 321
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 3
-Subparagraph (c)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479536/321-10-50-3

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